The present invention relates to transmitters for process control. In particular, the present invention relates to pressure transmitters which measure flow.
In process control, fluid movement through pipes is monitored by a series of process control transmitters connected to the pipes. The transmitters contain sensors that sense the difference between two pressures in a pipe (i.e. a differential pressure). From the differential pressure measurement, these transmitters infer the mass flow rate of the fluid in the pipe.
Generally, transmitters sense the differential pressure across an obstruction in the pipe. A typical obstruction is an orifice plate, which is a perforated disk inserted into the pipe. Although such disks provide a large and easily sensed pressure drop, they complicate the mass flow rate calculation because a number of compensation factors must be added to the calculation to account for fluid flow disruptions created by the disk. The disks also cause a substantial loss in pressure in the pipe. This reduction in pressure constitutes a needless and costly waste of energy.